Control rod end plug with a stabilizing configuration

Abstract

A nuclear reactor includes a plurality of upstanding guide thimbles and a plurality of control rods received in the guide thimbles and supported for movement relative to the thimbles between inserted and withdrawn positions. The control rods each include a tubular cladding member and an end plug attached to a lower end of the member. The improvement relates to the end plug having a stabilizing configuration which reduces lateral vibratory motion and contact between the control rod and its respective guide thimble. The end plug has an asymmetrical shape which places its terminal tip end in a position offset to one side of the central axis of the control rod and its end plug. As a result of interaction of the asymmetrical plug tip with coolant flowing along the control rod, a lateral steady-state force is imparted to the end plug which maintains the control rod end plug pressed against the wall of tis respective guide thimble. Several different asymmetrical configurations can be employed on the end plug.

We claim: 
     
       1. In a nuclear reactor including at least one guide thimble and at least one control rod received in said guide thimble and supported for movement relative thereto, the improvement which comprises: an end plug having a central axis and an imperforate asymmetrical tip configuration attached to an end of said control rod, said asymmetrical tip configuration defining a lower terminal end on said end plug which is offset to one side of said central axis and produces, in response to axial flow of coolant along said control rod and within its respective guide thimble, a non-symmetric coolant flow velocity pattern about said end plug and a lateral substantially steady state force on said control rod which presses said control rod end plug against a wall of said guide thimble so as to substantially prevent lateral vibration of said control rod due to said axial flow of the coolant.   
     
     
       2. The nuclear reactor as recited in claim 1, wherein said asymmetrical tip configuration includes a flat formed on a side of a generally tapered outer surface of said end plug tip so as to begin at an upper portion of said end plug on an opposite end of said central axis, intersect said central axis and terminate at said lower terminal end on said one side of said central axis. 
     
     
       3. The nuclear reactor as recited in claim 1, wherein said asymmetrical tip configuration includes a pair of flats formed on opposite sides of a generally tapered outer surface of said end plug, one of said flats intersecting said central axis of said end plug and meeting said other of said flats at said lower terminal end on said one side of said central axis. 
     
     
       4. The nuclear reactor as recited in claim 1, wherein said asymmetrical tip configuration includes a pointed conical surface which terminates at said offset lower terminal end of said end plug. 
     
     
       5. The nuclear reactor as recited in claim 1, wherein said asymmetrical tip configuration includes a concave surface formed on a side of a generally tapered outer surface of said end plug so as to begin at an upper portion of said end plug on an opposite side of said central axis, intersect said central axis and terminate at said lower terminal end on said one side of said central axis.